In many applications for purified process gases there is an increased need for higher levels of purity. This need is acutely felt in the semiconductor fabrication industry, where increasing control and precision in the processing environment require electronic gases that are exceedingly pure. However, the demand for higher purity gases has to be balanced with the cost and reliability of the systems used to supply those gases.
For example, the semiconductor industry needs increasingly pure sources of acetylene gas to fabricate carbon containing components such as dielectric films and photolithographic masks. Acetylene is filled in cylinders containing a porous substance saturated with solvent, such as acetone or dimethylformamide (DMF). The solvent in conjunction with the porous substance increases the capacity of the storage cylinders and helps stabilize the gas by dissolving acetylene gas. However, when the acetylene is discharged from the cylinders, vapors of the solvent also accompany the acetylene gas. The solvent vapors are the largest component of impurities, among other impurities in acetylene gas. Moreover, as the acetylene is being removed from the storage cylinder its concentration in the cylinder drops relative to the concentration of the solvent. This results in an increasing concentration of the solvent impurities in the starting acetylene over the lifetime of the cylinder. The solvent impurity along with its increasing concentration over time in the acetylene gas leads to upsets in certain semiconductor fabrication processes that use acetylene gas. Since the semiconductor fabrication processes are very sensitive to the changing concentration of solvent impurity in the acetylene gas, the cylinder usage is limited to the region where solvent concentration is low and constant in the gas, which results in frequent cylinder change outs and waste of gas.
In certain cases, the acetylene gas stored in cylinders could be passed through an on-site filter to remove solvent impurities before being used in an application. The filters are placed downstream of the storage cylinder and designed to remove the solvents so that only purified acetylene gas reaches the fabrication application. Delivering purified acetylene with consistently low solvent impurities is challenging because the amount of the impurities that need to be removed is significant, and changes over time. Thus, the purifier has to accommodate changing impurity levels in the starting acetylene to produce a purified gas with a constant low level of the impurities.
Because the solvent impurities are intentionally added to the acetylene, they are present in relative large quantities in the source gas, which places significant stress on the purifier to keep the impurity concentrations low in the purified product. It is typical for the purifier material to saturate or be consumed before an application run has been completed, forcing the run to shut down prematurely to regenerate or replace the purifier. These shut downs cause a significant decrease in the productivity of the fabrication process. As the thresholds for acceptable impurity levels keep going lower, the shut downs become more frequent. Thus, there is a need for new methods and systems to produce highly pure process gases with constant low levels of solvent impurities, decreasing frequency of cylinder change-outs, and increasing usage of the stored gases. These and other problems are presently addressed.